IGN released an article last week which summarizes the news that was announced at the Korra panel at SDCC.

Besides the facts that were already mentioned at the panel, the creators revealed that there will be something special in Book 2 and it will be "the most flashback-y of flashbacks." Whether it will be an episode consisting entirely of flashbacks alone, we won't know till the episode airs. They also did hint that Avatar Aang might appear again in Book 2.

The romance arcs in Korra will also be explored and the creators said Mako and Korra are still together but their jobs make things complicated and they try to maintain their relationship. As for Bolin, Mike DiMartino said that the earthbender will be involved in a bizzare love story. Let's hope things work out well for everyone.

Last but not least, we will be learning more about the legacy of the Avatar. It will be interesting to see how the first Avatar came about.